The present invention relates to a heat pump, a method of recovery of energy in the heat pump and a method of curtailing the power required for driving a compressor in the heat pump.
Compression-type heat pumps comprise an evaporator which absorbs heat energy from a lower temperature heat source, a compressor which adiabatically compresses the working fluid vapor evaporated by the evaporator, a condenser which provides heat energy to a higher temperature heat sink by condensation of heat medium vapor having a temperature and a pressure raised by the compressor, and an expansion valve which flashes and expands the heat medium condensate formed in the condenser, wherein an arrangement is made such that from the expansion valve, the working fluid is sent back to the evaporator.
Where the output required is relatively small (for example up to about 500 kw), use is made as the compressor of one of displacement compressors such as reciprocating displacement compressors, rotating displacement compressors (including screw type ones) and so forth. Displacement compressors are simple in structure and, in addition, can provide a constant pressure ratio even under partial loading conditions by changing the number of rotation, so that they are suitably useful in or for heat pumps or heat pump systems. However, the volume of fluid that they can deal with is relatively limited and also their volume efficiency tends to lower under partial loading conditions, whereby it has been difficult to realize a scale-up of heat pumps with use of a displacement compressor.
Then, where a relatively large output is required, use is made primarily of a centrifugal-type compressor since centrifugal-type compressors characteristically have a large capacity of fluid compression in spite of their being relatively limited in size.
Whereas conventionally heat pumps have been utilized mainly for air conditioning purposes, lately it has been increasingly attempted to make use of heat pumps also in various industrial fields by elevating the operation or working temperature and enhancing the operation efficiency of the heat pump. The present invention is in line with such tendency in the art and seeks for effectively elevating the operation or working temperature of the heat pump up to about 300.degree. C., which conventionally has been about 100.degree. C. at the highest, and providing a heat pump which can satisfactorily stand practical uses even if a large extent of rise is made of the temperature so as to largely broaden the field of application or use of heat pumps.
Generally, as the temperature difference to be set between a (lower temperature) heat source and a heat sink is greater, the power required for driving the compressor becomes greater and the coefficient of performance (the ratio of transferred heat to the power input for the driving of the compressor -hereinafter referred to as COP-) becomes lowered.
Thus, although there have been attempts made to utilize heat pumps in industrial fields, it is difficult to attain a sufficient effect of energy saving in addition to the difficulty that it is costly to install a heat pump, and in many instances no high effect has been provided of the economical advantage and the investment, with the result that today still limited are the fields in which heat pumps are put for an actual or a practical use.
Also, whereas in order to adapt the heat pump to a high temperature operation, use is made of water for the heat medium or working fluid, now that vapor is adiabatically compressed to make it a superheated vapor or steam, it is necessary to appropriately adjust the degree of superheating.